Self-cleaning surfaces for particleladen atmospheres



R. F. WIGGINS Feb. 24, 1970 SELF-CLEANING SURFACES FOR PARTICLE-LADENATMOSPHERES Filed May '7, 1968 INVENTOR RICHARD E WIGGINS ATTORNEYSUnited States Patent "ice 3,496.856 SELF-CLEANING SURFACES FOR PARTICLE-LADEN ATMOSPHERES Richard F. Wiggins, Fairfield, Coun., assignor to TheGyromat Corporation, Stratford, Conn., a corporation of ConnecticutFiled May 7, 1968, Ser. No. 727,303 Int. Cl. F241? 13/02 US. CI. 9833 6Claims ABSTRACT OF THE DISCLOSURE The present disclosure relates toself-cleaning surfaces such as non-drip panels, curtains, and the likefor use in spray booths and other areas where avoidance of problemsattributable to accumulation of overspray and dripping is desired. Thenew self-cleaning or non-drip structures generally comprise a dry,porous static boundary, such as ordinary sailcloth, which has onesurface exposed to the spray particle-laden atmosphere and the othersurface subjected to a continuous flow of pressurized air. A dynamicboundary layer of permeating air is established at the exposed side ofthe porous boundary, which dynamic boundary layeris effective inpreventing the deposition of sufficient spray particles on the exposedsurface of the boundary to form drippable drops. The non-drip structuresmay assume the form of an entire wall or entire ceiling of a spraybooth, or they may be limited to a relatively small unit area of a spraybooth, or even to a unit area of spray equipment (whether in a booth ornot) for use in combatting and eliminating contamination and drippingproblems.

BACKGROUND OF THE INVENTION In the coating of products by spraytechniques, electrostatic, pneumatic, or otherwise, it is the majorobjective of the spray coater to deposit an absolutely uniform coatingfree of streaks, drops, or other imperfections. While in certainapplications one or more of these types of imperfections may betolerated or unnoticed, many product application require an absolutelyuniform layer of coating material to be applied, and there is a criticalrequirement that the applied coating be free of drip marks i.e., theirregularities in a coating occasioned by drops of accumulated spraymaterial which have been deposited on a workpiece by falling from asurface of the spray booth.

Therefore, it is an object of the present invention to provide spraybooth surfaces which are effectively drip free and non-contaminating ofuniformly sprayed work surfaces. It is still another object of theinvention to provide spray booth surfaces which are self-cleaning andwhich will contribute to the overall cleanliness of a spray booth.

SUMMARY OF THE INVENTION The provision of drip free or self-cleaningsurfaces in a spray booth or the like, may be effected in accordancewith the principles of the present invention by lining the walls andceiling of a spray booth with porous boundary forming layers, such asconventional sailcloth, i.e., a heavy canvas or duck fabric normallyused for sails, tents, etc. More specifically, the sailcloth is arrangedsuch that the inner surfaces thereof constitute at least a portion of aclosed plenum chamber. The circulation of pressurized air through thechamber prevents the accumulation of drip forming spray particles on thesurfaces of the sailcloth exposed within the spray booth and subjectedto the spray filled atmosphere. Enough of the pressurized air 3,496,856Patented Feb. 24, 1970 permeates the cloth boundary to establish eddycurrents at the exposed surfaces, which currents prevent the depositionof sufiicient spray particles thereupon to form drippable drops. As willbe appreciated, the new arrangement may be aptly characterized asself-cleaning as well as drip free.

DESCRIPTION OF THE DRAWINGS For a better understanding of the presentinvention and a more complete appreciation of the attendant advantagesthereof, reference should be made to the following detailed descriptiontaken in conjunction with the accompanying drawings, in which FIG. 1 isa perspective view of a paint booth, including non-drip wall surfaces,embodying the principles of the present invention; and

FIG. 2 is a cross-sectional view showing details of construction of thenew and improved drip-free and selfcleaning surfaces of a spray chamber.

DESCRIPTION OF THE INVENTION Referring to FIG. 1, the drip-free,self-cleaning surfaces of the present invention are incorporated inconventional spray booths or spray chambers 10. A typical booth includesa floor 11, side walls 12, and a ceiling 13, and has at least one spraystation 14 at which articles A are sprayed with atomized coatings ofspray material by a spray gun 15. An exhaust duct 17 is provided to ventthe spray-laden atmosphere of the booth, and, advantageously, a conveyorsystem (not shown) may be employed to transport the articles A into andout of the spray booth.

As will be understood, there exists in any booth considerable amounts ofoverspray (atomized spray particles) which are not deposited on theworkpiece. Regardless of the efliciency of the exhaust system, thisoverspray tends to accumulate on booth wall surfaces, especially aceiling surface, and droplets of spray material tend to build up andeventually drip off the surface to contaminate the booth or, worse yet,to form drip marks on the articles being coated.

In accordance with the principles of the invention, the surface areas ofa spray booth, upon which overspray tends to accumulate and form drops,are provided with non-drip, self-cleaning auxiliary surfaces. Morespecifically, and as shown in FIG. 2, each non-drip surface is a dryporous layer 18, advantageously fabricated from sailcloth which issecured to the booth wall by mounting strips 19 and screws 19' or othersuitable fasteners, to define a collapsed plenum chamber 20 therewith.As shown in the illustrated embodiment, the chambers 20 are collapsibleand cover the entire wall and ceiling surfaces of the booth, but thechambers may be of rigid construction and/or they may be limited tosmaller surface areas when desired or found necessary. In any event, theplenum chambers 20 are provided by a pneumatic supply tube 21 with aconstant flow of air under predetermined pressure. The air effectivelyinflates the plenum chamber 20 and is delivered in sufficient quantityand under sufficient enough pressure to the internal surfaces 18a .ofthe porous boundary layer 18 to steadily permeate therethrough to theexternal or exposed surfaces 18b. In accordance with the principles ofthe invention, the steadily permeating air will establish a dynamicboundary layer which will tend to prevent the accumulation of oversprayparticles on the static boundary layer 18. Thus the permeating air(which need only be under low pressure to permeate sailcloth)effectively renders the surfaces 18b self-cleaning by repelling sprayparticles therefrom and eliminates any possibility of droplets of sprayforming and subsequently dripping on articles A. As will be understood,the spray-laden or misty atmosphere of the booth is itself constantlyvented through existing exhaust systems such as the duct 17.

The non-drip, self-cleaning surfaces 18 of the invention may be employedin those areas of any spray booths in which droplet buildup occurs.Since air circulation is not the same from booth to booth due to manyfactors, the specific placement of the new and improved non-dripsurfaces in a particular booth will be on an empirical basis.

As will be appreciated, the utilization of the nondrip, self-cleaningsurfaces .of the present invention will greatly alleviate problems ofcontamination of spray booth surfaces and the marring of sprayedsurfaces by drip marks.

It should be understood that the specific form of the non-drip,self-cleaning surfaces herein illustrated and described is intended tobe representative only, as certain variations may be made thereinwithout departing from the clear teachings of the disclosure. Forexample, the new surfaces may assume the form of spray gun enclosures orsurfaces to protect spray apparatus within or without a spray booth.Likewise, the new surfaces may be used in atmospheres laden withparticles other than spray particles, e.g., dust. Accordingly, referenceshould be made to the following appended claims in determining the fullscope of the invention.

What is claimed is:

1. A self-cleaning, drip-free surface comprising:

(a) a supporting structure having a continuous air impervious surface,

(b) a porous boundary layer having inner and outer surfaces,

() means uniting said boundary layer with said air impervious surface todefine a closed plenum chamber, and

(d) means for introducing a gas at greater than atmospheric pressureinto said plenum chamber;

(e) whereby a steady flow of gas from the plenum chamber to the outersurface of said porous boundary layer is established.

2. A self-cleaning, drip-free surface in accordance with claim 1, inwhich:

5 (a) said boundary layer is supported loosely relative to saidstructure and said chamber is thereby inflatable,

(b) said layer is adapted to be expanded upon the inflation of saidchamber.

. 3. A drip-free, self-cleaning surface in accordance with claim 1, inwhich:

(a) said porous layer comprises a woven fabric. 4. A drip-free, selfcleaning surface in accordance with claim 3, in which:

(a) said fabric is sailcloth.

5. A wall structure, comprising:

(a) a porous panel means forming an inside wall surface of a booth orthe like, and

(b) air supply means to provide and maintain air at greater thanatmospheric pressure on the outside surface of said porous panel means,

(0) said air supply and said porous panel means being so related as toprovide a general inward flow of air through the porous panel tominimize the deposition on said wall of spray material.

6. The wall structure of claim 5, in which: (a) said porous panel meanscomprises a flexible,

fabric-like material.

References Cited UNITED STATES PATENTS 1,167,249 1/1916 Arel 98-892,105,108 1/1938 Crosley 9889 2,702,503 2/1955 Wildhaber 98-33 LLOYD L.KING, Primary Examiner

